Do not use the default LINK_FLAGS value for windows builds, the default
"-E" linker option only causes warnings for MinGW since it's essentially
ignored by the linker.
The flag is also unneeded since linking plugins against the gkrellm
binary is not done on win32 so none of the gkrellm/gkrellmd functions
need to be exported, the API is manually exposed via the win32-specific
libgkrellm/libgkrellmd static libs.